Compartmentation of roof voids above self contained flats

[Seetek]

Just to pick this up again.

Would you consider that any form of retrospective cavity barrier is required if the floor within an open communal roof void is a concrete slab?

Obviously there is potential for fire spread across the open void but little chance of ingress into the flats.

I would think cavity barriers would be needed as per ADB in this case. A similar scenario is discussed in the specialised housing guide, although different premises, the same principle would apply IMO.

[Fishy]

...Systems are now available in which ceilings and floors can be upgraded to provide an hours FR from above and below and meet BS 476;pt 21 criteria...

We'd be very interested in these (do tell who offers them)... British Gypsum used to do a variation of their 'MF' ceiling but they're reluctant to offer formal evidence of fire performance for it these days.  I also thought you couldn't test a ceiling/floor from above to below under BS 476: Part 21 (only under the EN standards), but I'd be quite prepared to be proven wrong.

I wouldn't use it for resi, but we do have situations in non-domestic premises where corridor walls haven't been built up to the soffit (depressingly common) where it might be useful.

[William 29]

You also need to consider the risk of a fire breaking out of a window, affecting the eves and getting into the roof that way. Also external fire on the roof due to hot works etc.